Ultraviolet (UV) radiation is part of the electromagnetic spectrum that reaches the earth from the sun and has wavelengths shorter than visible light. These wavelengths are classified as UVA (320-400 nm), UVB (280-320 nm), or UVC (100-280 nm). While most UVC is absorbed by the ozone layer and does not reach the earth, both UVA and UVB can penetrate the atmosphere and have important health consequences.
Overexposure to UV radiation is the major risk factor for the development of skin cancer, which is the most common form of cancer in the United States. In addition, increased exposure to sun irradiation has been linked to immune suppression and eye damage. On the other hand, UV radiation in sunlight can also affect people's health in beneficial ways. In particular, sunlight is the major source of vitamin D producing UVB radiation, which has a wide range of positive health effects. Vitamin D production is not only important to prevent osteoporosis and osteomalcia, but also may decrease the incidence of diabetes, reduce the mortality from various cancers, among many other health benefits. However, a number of studies have shown that most American children, adolescents, and adults may not go outside enough to meet their vitamin D needs. Therefore, there has been a growing consensus among a number of public health organizations that there needs to be a balance between the risks of having too much and the risks of having too little sunlight.
UV index (UVI) is an internationally accepted parameter for measuring the intensity of UV radiation. However, measuring UVI alone is insufficient to determine if a person receives too little or too much UV exposure. The actual UV irradiation dose received by a person is not only affected by the UVI, but also affected by many other factors, such as the duration of UV exposure, the applied sunscreen, etc.
Most existing UV measurement instruments are ground based. While these instruments can provide broadband measurement of UV irradiance received by the UV sensor at the ground level, such a measurement is unlikely to reflect the actual UV irradiance received by individuals in the same area. Environmental factors such as cloud cover, tree or building shade, reflections from water, sand, snow, building, etc, as well as personal choices such as sunscreen usage can have substantial impact on the actual dose absorbed by the individual. Efforts have been made in recent years to develop wearable UV measurement devices. However, these UV measurement devices have a number of shortcomings, including but are not limited to: the device is cumbersome and not convenient for daily wearing; the device is not waterproof; the device can only measures the UVI, not the actual UV dose; the UV measurement does not take into account factors affecting skin UV absorption such as clothing coverage, skin color, sunscreen usage, sensor location, etc.; the device lacks capabilities for data storage, editing, analysis, and reporting; and the device lacks networking capability.
UV radiation in sunlight can also affect people's health in beneficial ways, in particular, vitamin D production. Many people do not get sufficient vitamin D from dietary sources, so sunlight-derived vitamin D is their primary source. However, because of the fear of developing skin cancer, many people avoid sunlight whenever possible and wear protective clothing and sunscreens. As a result, many people have vitamin D insufficiency. So far, there is no objective measure on the actual UV dose received by a person and how much vitamin D has been produced by the UV radiation. Thus people are unaware of whether they received too much or too little sunlight, and not sure how much vitamin D supplement should be taken—if it is needed at all.
Currently there is no information about the level of UVI at different places in real time, which could help people prepare or avoid exposing to a high UVI area. Although some weather stations might have a forecasted UVI data, the forecast is based on modeled simulation for a large geometrical area, and lacks both spatial resolution and temporal resolution. Moreover, there are several factors that make that data inaccurate. For example, the forecasted UVI does not include the effects of atmospheric pollutants or haze which can substantially decrease UV intensity, especially in urban areas. The forecast does not take into account variable surface reflection (e.g., sand, water, or snow), which can substantially increase individual's exposure at the beach or on ski-slopes.
Although there are some efforts to develop wearable UV measurement devices, these devices have a number of shortcomings. For example, the existing UV devices do not have the indications of device circuitry such as battery status, local memory status and electronic leash status, which could result in a delay of application program functions especially when some immediate actions such as user notification is needed. The sampled UV data could be lost, if the battery is running low or the local memory is full. In addition, multiple users could not share the same hardware since the user information is stored in the specific hardware. Many wearable UV measurement devices are for designed for single-user purpose. Parents wanting to monitor several children at the same time or a person who wants to measure UV at several different locations have to use multiple devices. Moreover, there is no intuitive summary for the users to understand their UV dose, and there is a lack of user editing or programming function. Furthermore, the operation of these devices is not convenient and user friendly.
The shortcomings of the existing UV measurement devices are solved by the present invention as described below. The unique advantages of the present invention will be appreciated by people of ordinary skill in the art after referring to the written description of the invention in conjunction with the illustrative drawings.